The Effect of Polyethylene Packaging and Hot Water Treatment on Shelf Life and Quality of Pomegranate Fruits Cultivar (Poost Nazuk Kandahar)

Pomegranate (Punica granatum L.) is an important fruit crop of the world which native to Iran and Afghanistan. Pomegranate is produced throughout the Afghanistan. However, the most pomegranate orchard is in the south-west and the west region of Afghanistan, in the provinces of Kandahar, Helmand, Nimroz, Farah, Kapisa, Nangarhar and Herat. The major storage problems are desiccation of the fruit resulting in a brownish colored tough peel and arils, weight loss, chilling injury and fungi decay. Further, the storage temperature recommended for pomegranates has varied from 0 to 10°C from two weeks to seven months depending on the cultivar. Storing pomegranate at low temperature with packaging minimized chilling injury and maintained fruit quality. Heat treatment causes changes in fruit ripening, such as the inhibition of ethylene synthesis and action of cell wall degrading enzymes, due to changes in gene expression and protein synthesis. Pre-storage hot water treatment increases fruit quality and reduce fruit weight loss and chilling injury in pomegranate.

Fully mature, pomegranate (Punica granatum L.) fruits cv. ‘PoostNazuk Kandahar’ was harvested form Kandahar province in 2014. They were immediately transported by plane to the laboratory of Horticultural Science, Ferdowsi University of Mashhad Iran. After washing and initial measurements, half of fruits were immersed in a hot water (50 and 25°C) bath for three minutes. Hot water treatment fruits were packaged in plastic zippers and the others half were without packaging. All the treated fruits were transferred to cold storage at 5±1°C and a relative humidity of 85 to 90% for four months. Every 30 days each the physicochemical characteristics of pomegranate were evaluated. Experimental design was split factorial by completely randomized design with four replications. All analyses were performed with statistical software (JMP. 8.0, 2009).

The results demonstrated that the combination of hot water (HW) and polyethylene packaging was more effective in extending shelf life and reducing pomegranate fruit decay than the application of each treatment alone during long-term cold storage. The HW (50°C) treatment in combination with polyethylene packaging had significant effect (p< 0.01) on fruit weight loss and chilling injury index (CI) compared with the water (25°C) and without packaging during storage time. Most of fruit weight loss and CI were 37% and 24.7% that related to water (25°C) treatment and non-packaging, and the lowest were in order 1.6% and 2.2 % related to polyethylene packaging and HW (50 C°) treatments. Reduction in weight loss and CI by polyethylene packaging have been reported by other researchers [3, 4, 5, 9, 25 and 31]. HW (50°C) treatments reduced the expanding of fungi decay significant (p< 0.01) caused by use of polyethylene packaging after four months storage. This is agreement with Talaie et al [4], Artés et al [5] and Moradinezhad and Khayyat [31]. The effect of packaging on total phenolic compounds was also significant (p< 0.01). The total phenolic compounds of pomegranates showed an increase during the 120 days storage. Fruit without packaging had higher (443.25 mg/Lit) total phenolic compounds than the fruit stored in polyethylene package (332 mg/Lit), reaching a maximum accumulation, which is in agreement with the findings of other researchers [15, 24, and 38]. The HW treatment alone or in combination with packaging had no significant effect on TSS, TA and pH as compared to the water (25°C) and without packaging. At the end of storage, there was a significant increase in TSS and pH, and significant decreased in TA fruit juice after 4-month storage. Our finding is in agreement with previous reports [4, 5, 25 and 34], however was in contrast with the results of Nanda et al [33] who reported higher retention of TA in shrink film wrapped pomegranates, when compared to control fruit. One of the reasons for increase in TSS probably is decrease of fruit juice and its increase in concentration, during the storage time [1]. Rastegari et al [2] reported the increase in pH of fruit juice during storage, which is probably due to the breakdown of organic acids during the respiratory process.

Combined pre-storage treatments of HW and polyethylene package have more benefits than their individual application on maintaining quality and extending pomegranate fruit shelf life in prolonged cold storage. The pomegranate fruit cv. ‘PoostNazuk Kandahar’ could be stored for at least 20 weak under this combined treatment, effectively extending their marketing period with less decay. However, the unpackaged fruit, spoiled totally by 13 weak. Therefore, it is concluded that a combination of HW and polyethylene package treatment is a simple and low-cost method that has the ability to improve quality and postharvest life of pomegranate fruit cv. ‘PoostNazuk Kandahar’ during cold storage. However, more research is needed in this regard.